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Plastic pollution poses a significant environmental challenge, necessitating the investigation of bioplastics with reduced end-of-life impact. This study systematically characterizes four promising bioplastics-polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polylactic acid (PLA). Through a comprehensive analysis of their chemical, thermal, and mechanical properties, we elucidate their structural intricacies, processing behaviors, and potential morphologies. Employing an environmentally friendly process utilizing supercritical carbon dioxide, we successfully produced porous materials with microcellular structures. PBAT, PBS, and PLA exhibit closed-cell morphologies, while PHBV presents open cells, reflecting their distinct overall properties. Notably, PBAT foam demonstrated an average porous area of 1030.86 μm 2 , PBS showed an average porous area of 673 μm 2 , PHBV displayed open pores with an average area of 116.6 μm 2 , and PLA exhibited an average porous area of 620 μm 2 . Despite the intricacies involved in correlating morphology with material properties, the observed variations in pore area sizes align with the findings from chemical, thermal, and mechanical characterization. This alignment enhances our understanding of the morphological characteristics of each sample. Therefore, here, we report an advancement and comprehensive research in bioplastics, offering deeper insights into their properties and potential morphologies with an easy sustainable foaming process. The alignment of the process with sustainability principles, coupled with the unique features of each polymer, positions them as environmentally conscious and versatile materials for a range of applications.

Alginate dialdehyde and l-lysine-functionalized alginate dialdehyde were prepared to provide active aldehyde and l-lysine sites along the alginate backbone, respectively. Different concentrations of substrates and the reduction agent were added, and their influence on the degree of l-lysine substitution was evaluated. An amination reduction reaction (with l-lysine) was conducted on alginate dialdehyde with a 31% degree of oxidation. The NMR confirmed the presence of l-lysine functionality with the degree of substitution of 20%. The structural change of the polymer was observed via FTIR spectroscopy, confirming the formation of Schiff base covalent linkage after the crosslinking. The additional l-lysine sites on functionalized alginate dialdehyde provide more crosslinking sites on the hydrogel, which leads to a higher modulus storage rate than in the original alginate dialdehyde. This results in dynamic covalent bonds, which are attributed to the alginate derivative-gelatin hydrogels with shear-thinning and self-healing properties. The results suggested that the concentration and stoichiometric ratio of alginate dialdehyde, l-lysine-functionalized alginate dialdehyde, and gelatin play a fundamental role in the hydrogel's mechanical properties.

A solvent-free route of initiated chemical vapor deposition (iCVD) was used to synthesize a bio-renewable poly(α-Methylene-γ-butyrolactone) (PMBL) polymer. α-MBL, also known as tulipalin A, is a bio-based monomer that can be a sustainable alternative to produce polymer coatings with interesting material properties. The produced polymers were deposited as thin films on three different types of substrates-polycarbonate (PC) sheets, microscopic glass, and silicon wafers-and characterized via an array of characterization techniques, including Fourier-transform infrared (FTIR), proton nuclear magnetic resonance spectroscopy ( 1 H NMR), ultraviolet visible spectroscopy (UV-vis), differential scanning calorimetry (DSC), size-exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Optically transparent thin films and coatings of PMBL were found to have high thermal stability up to 310 °C. The resulting PMBL films also displayed good optical characteristics, and a high glass transition temperature ( T g ~164 °C), higher than the T g of its structurally resembling fossil-based linear analogue-poly(methyl methacrylate). The effect of monomer partial pressure to monomer saturation vapor pressure ( P m /P sat ) on the deposition rate was investigated in this study. Both the deposition rate and molar masses increased linearly with Pm/Psat following the normal iCVD mechanism and kinetics that have been reported in literature.

In this work, two novel routes to synthesis cross-linked polypropylene (PP) are introduced by using two different precursors (2-thiophenemethyl amine (TMA) and 1-(3 aminopropyl) imidazole (API)), both cross-linked with 1,1'-(methylenedi-4,1-phenylene) bismaleimide (BM) at two different annealing temperature values ( T = 50 °C and T = 150 °C). Both Diels-Alder (DA) and Michael addition reactions were successfully performed with TMA and API, respectively, albeit with different reactivity. Imidazole clearly shows a higher reactivity compared to thiophene. In addition, an increase in annealing temperature leads to a higher degree of cross-linking. The highest degree of cross-linking was obtained by the imidazole product after annealing at 150 °C (IMG1A150) as evident from the highest complex viscosity (|η*|) value of IMG1A150. A difference in rheology and thermal properties between the imidazole and thiophene cross-linked products was also observed. However, both products have superior melt properties and thermal stability compared with the starting material. They show processability at high temperatures. The melt flow behavior and de-cross-linking at higher temperatures can be tuned depending on the choice of imidazole or thiophene. This study shows an advance on the cross-linked PP processing and its product performances for further application on the commercial scale.

In this work, the possibility of preparing cross-linked polypropylene (PP) via Diels−Alder (DA) chemistry is explored. The overall strategy involves reaction of maleated polypropylene (the starting material), furfuryl amine (FFA), and bismaleimide (BM) as the cross-linking agent. The occurrence of reversible cross-linking was studied by checking the presence of relevant peaks in FTIR spectra, i.e., CH out-of-plane bending vibrations of the furan ring’s peak (γCH) at an absorption band of 730−734 cm−1, CH=CH of the BM aromatic ring’s stretching vibrations (υCH=CH) at an absorption band of 1510 cm−1, and the DA adduct (C-O-C, δDAring) at an absorption band of 1186 cm−1. In agreement with the spectroscopic characterization, the presence of a cross-linked network is also confirmed by rheology, namely the higher storage modulus (G′) compared with loss modulus (G″) value (G′ >> G″), as obtained via temperature sweep. Both the maleic anhydride (MA) content as well as the annealing temperature (50 °C and 120 °C) favor the DA reaction, while only partial de-cross-linking (retro DA) is observed at the higher temperature range of 150−200 °C. In addition, the products show higher mechanical robustness and thermal stability compared to the starting material.

Nowadays, the self-healing approach in materials science mainly relies on functionalized polymers used as matrices in nanocomposites. Through different physicochemical pathways and stimuli, these materials can undergo self-repairing mechanisms that represent a great advantage to prolonging materials service-life, thus avoiding early disposal. Particularly, the use of the Joule effect as an external stimulus for self-healing in conductive nanocomposites is under-reported in the literature. However, it is of particular importance because it incorporates nanofillers with tunable features thus producing multifunctional materials. The aim of this review is the comprehensive analysis of conductive polymer nanocomposites presenting reversible dynamic bonds and their energetical activation to perform self-healing through the Joule effect.

Among smart materials, self-healing is one of the most studied properties. A self-healing polymer can repair the cracks that occurred in the structure of the material. Polyketones, which are high-performance thermoplastic polymers, are a suitable material for a self-healing mechanism: a furanic pendant moiety can be introduced into the backbone and used as a diene for a temperature reversible Diels-Alder reaction with bismaleimide. The Diels-Alder adduct is formed at around 50 °C and broken at about 120 °C, giving an intrinsic, stimuli-responsive self-healing material triggered by temperature variations. Also, reduced graphene oxide (rGO) is added to the polymer matrix (1.6-7 wt%), giving a reversible OFF-ON electrically conductive polymer network. Remarkably, the electrical conductivity is activated when reaching temperatures higher than 100 °C, thus suggesting applications as electronic switches based on self-healing soft devices.

This article reviews some of the intrinsic self-healing epoxy materials that have been investigated throughout the course of the last twenty years. Emphasis is placed on those formulations suitable for the design of high-performance composites to be employed in the aerospace field. A brief introduction is given on the advantages of intrinsic self-healing polymers over extrinsic counterparts and of epoxies over other thermosetting systems. After a general description of the testing procedures adopted for the evaluation of the healing efficiency and the required features for a smooth implementation of such materials in the industry, different self-healing mechanisms, arising from either physical or chemical interactions, are detailed. The presented formulations are critically reviewed, comparing major strengths and weaknesses of their healing mechanisms, underlining the inherent structural polymer properties that may affect the healing phenomena. As many self-healing chemistries already provide the fundamental aspects for recyclability and reprocessability of thermosets, which have been historically thought as a critical issue, perspective trends of a circular economy for self-healing polymers are discussed along with their possible advances and challenges. This may open up the opportunity for a totally reconfigured landscape in composite manufacturing, with the net benefits of overall cost reduction and less waste. Some general drawbacks are also laid out along with some potential countermeasures to overcome or limit their impact. Finally, present and future applications in the aviation and space fields are portrayed.

Low cross-link density thermally reversible networks were successfully synthesized from jatropha and sunflower oils. The oils were epoxidized and subsequently reacted with furfurylamine to attach furan groups onto the triglycerides, preferably at the epoxide sites rather than at the ester ones. Under the same reaction conditions, the modified jatropha oil retained the triglyceride structure more efficiently than its sunflower-based counterpart, i.e., the ester aminolysis reaction was less relevant for the jatropha oil. These furan-modified oils were then reacted with mixtures of aliphatic and aromatic bismaleimides, viz. 1,12-bismaleimido dodecane and 1,1'-(methylenedi-4,1-phenylene)bismaleimide, resulting in a series of polymers with T g ranging between 3.6 and 19.8 °C. Changes in the chemical structure and mechanical properties during recurrent thermal cycles suggested that the Diels-Alder and retro-Diels-Alder reactions occurred. However, the reversibility was reduced over the thermal cycles due to several possible causes. There are indications that the maleimide groups were homopolymerized and the Diels-Alder adducts were aromatized, leading to irreversibly cross-linked polymers. Two of the polymers were successfully applied as adhesives without modifications. This result demonstrates one of the potential applications of these polymers.

In this work, we prepared electrically conductive self-healing nanocomposites. The material consists of multi-walled carbon nanotubes (MWCNT) that are dispersed into thermally reversible crosslinked polyketones. The reversible nature is based on both covalent (Diels-Alder) and non-covalent (hydrogen bonding) interactions. The design allowed for us to tune the thermomechanical properties of the system by changing the fractions of filler, and diene-dienophile and hydroxyl groups. The nanocomposites show up to 1 × 10 4 S/m electrical conductivity, reaching temperatures between 120 and 150 °C under 20-50 V. The self-healing effect, induced by electricity was qualitatively demonstrated as microcracks were repaired. As pointed out by electron microscopy, samples that were already healed by electricity showed a better dispersion of MWCNT within the polymer. These features point toward prolonging the service life of polymer nanocomposites, improving the product performance, making it effectively stronger and more reliable., Competing Interests: The authors declare no conflict of interest.

[2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) is a well-studied sulfobetaine-methacrylate as its zwitterionic structure allows the synthesis of polymers with attractive properties like antifouling and anti-polyelectrolyte behavior. In the present work, we report the Cu⁰-mediated living radical polymerization (Cu⁰-mediated LRP) of SBMA in sodium nitrate aqueous solution instead of previously reported solvents like trifluoroethanol and sodium chloride aqueous/alcoholic solution. Based on this, starch-g-polySBMA (St-g-PSBMA) was also synthesized homogeneously by using a water-soluble waxy potato starch-based macroinitiator and CuBr/hexamethylated tris(2-aminoethyl)amine (Me₆TREN) as the catalyst. The structure of the macroinitiator was characterized by ¹H-NMR, 13 C-NMR, gHSQC, and FT-IR, while samples of PSBMA and St-g-PSBMA were characterized by ¹H-NMR and FT-IR. Monomer conversion was monitored by ¹H-NMR, on the basis of which the reaction kinetics were determined. Both kinetic study and GPC results indicate reasonable controlled polymerization. Furthermore, a preliminary study of the thermal response behavior was also carried through rheological tests performed on aqueous solutions of the prepared materials. Results show that branched zwitterionic polymers are more thermal-sensitive than linear ones.

This work reports on the healing of early stage fatigue damage in ionomer/nano-particulate composites. A series of poly(ethylene- co -methacrylic acid) zinc ionomer/Fe₃O₄ nanoparticle composites with varying amounts of ionic clusters were developed and subjected to different levels of fatigue loading. The initiated damage was healed upon localized inductive heating of the embedded nanoparticles by exposure of the particulate composite to an alternating magnetic field. It is here demonstrated that healing of this early stage damage in ionomer particulate composites occurs in two different steps. First, the deformation is restored by the free-shrinkage of the polymer at temperatures below the melt temperature. At these temperatures, the polymer network is recovered thereby resetting the fatigue induced strain hardening. Then, at temperatures above the melting point of the polymer phase, fatigue-induced microcracks are sealed, hereby preventing crack propagation upon further loading. It is shown that the thermally induced free-shrinkage of these polymers does not depend on the presence of ionic clusters, but that the ability to heal cracks by localized melting while maintaining sufficient mechanical integrity is reserved for ionomers that contain a sufficient amount of ionic clusters guaranteeing an acceptable level of mechanical stability during healing.